With the electrical grid growing in complexity, finding the right operations and maintenance (O&M) strategy for substation assets is becoming increasingly important. O&M of substations and switchgear assures reliable supply and failure reduction. Asset management and maintenance is carried out when certain indicators give the signal that the equipment is deteriorating, and the probability of failure is increasing. Various strategies, whether time, condition or reliability based, can enable a drastic reduction of the costs associated with maintenance, thereby curtailing the incidence of serious faults, and optimising resources. An unpredicted breakdown in a substation or switchgear can lead to massive time and cost overruns for utilities. Substation asset maintenance also involves periodic planned inspections, checking, testing and troubleshooting to ensure the correct operation and interaction of all components over a plant’s life cycle.
O&M strategies
Various key maintenance strategies have been established over the years for the maintenance of the principal assets of substations.
Under time-based maintenance, typically, periodic maintenance is carried out according to the manufacturer’s generic maintenance schedule. This may also include the provision of spare parts and consumables, and the replacement of worn-out portions or systems during the substation’s service life.
For condition-based maintenance (CBM), maintenance is planned according to the condition of the equipment. CBM of substation assets can be undertaken through a combination of intelligent electronic devices, smart sensors, etc. Moreover, the actual condition of the equipment is constantly assessed through online detection of significant working device strictures, and their automatic comparison with average values and functioning parameters.
Reliability-based maintenance is another method that can be considered. Substation reliability modelling enables customers to comprehend the risk linked to each of its components. Reliability-centred maintenance is based on optimising maintenance investment by limiting the execution of redundant tasks while concentrating on the substation components that are representative of higher risk. This evaluation includes “failure mode and effect analysis” for determination of the best maintenance strategy to retain reliability. Furthermore, the life cycle cost-based evaluation of this approach has to be derived from CBM analysis.
For switchgear power systems, maintenance strategies are broadly similar and can be preventive, corrective, or, less commonly, predictive. Preventive maintenance is key to keeping a system working properly, and entails regular, annual inspection of components. Further, the components should be tested to ensure smooth functioning, since even slight uninterrupted vibrations can damage the equipment. Predictive maintenance methods are useful for condition-based monitoring of switchgear equipment and are also used for determining when switchgear maintenance is required. Maintenance processes are commenced based on different parameters, different methods for acquiring the condition data and, most importantly, an understanding of the degradation mechanisms that have an impact on switchgear. Therefore, intrusive and non-intrusive diagnostic tests can be conducted on switchgear. Tests should be undertaken at the time of commissioning to establish a baseline for future judgement.
The health of gas-insulated substation (GIS) equipment can be supervised in several ways depending on various purposes and needs. Gas monitoring is predominantly used to make sure that adequate sulphur hexafluoride (SF6) gas is provided for meeting the equipment’s requirements, typically concerning some arrangement of gas density monitoring. Apart from being a very good insulator, SF6 is a potential greenhouse gas, and therefore its leakage into the environment also needs to be strictly monitored. Partial discharge in the SF6-filled switchgear chambers can reduce the life and quality of insulation.
The most frequent monitoring arrangement is typically gas monitoring, but gas density measurements also have certain limitations. An online SF6 system typically comprises a gas density sensor, a data capture and processing platform, and graphical user interface software. Partial discharge monitoring has also received interest, as it promises the possibility of sending out warnings related to insulation problems in GIS installations. A GIS needs to be partial discharge-free. Any detection of such discharge above a minimum threshold is construed as an emergent difficulty. With the help of online partial discharge monitor servers, data is collected from the sensor nodes and analysed. Installed software automatically translates the partial discharge movement into graphs and management reports, showing its severity, location and type. Online partial discharge monitoring allows constant monitoring of the power transformer or GIS while it is operating. This allows maintenance and operations to receive partial discharge data in real time. In comparison, offline partial discharge monitoring can be carried out when the GIS is taken offline during a scheduled outage or a normal maintenance cycle. Several technologies can be used to monitor partial discharge today. Acoustic, dissolved gas analysis and ultra high frequency technologies are the most common. Accurate interpretation of partial discharge data is essential to maintenance planning.
Conclusion
Optimising the life of ageing switchgear is not a new concern, but it continues to be a major issue for the power industry. Substations and switchgear are key elements in power systems and play a crucial role in overall business performance. Well-planned substation and switchgear maintenance ensures reliable supply and reduction in failures. A major failure can result in significant time and cost overruns. This makes it imperative to take optimised maintenance and replacement decisions by moving from reactive to proactive maintenance, thereby reducing unplanned downtime and minimising the costs of extending asset life.
When it comes to asset management, some of the governing constituents of operating costs are maintenance and associated costs. In addition, other decisive parameters must be recognised along with their impact on the overall cost. Getting into an annual inspection routine can potentially forestall expenditure on new equipment installation or repairs, while simple maintenance processes can prolong equipment life by decreasing the likelihood of malfunctioning. Switchgear apparatus characteristically requires a low level of maintenance.